1. Field of the Invention
The present invention relates to a piezoelectric element having a metal oxide ferroelectric film applicable to various dielectric devices by electric and/or optical properties, an ink jet recording head utilizing the same and a producing method for a piezoelectric element.
2. Related Background Art
A piezoelectric element is constituted of a crystalline piezoelectric ceramic material of a ferroelectric or paraelectric property. The piezoelectric ceramic material generally has a two-component composition principally constituted of lead zirconate titanate (hereinafter represented as “PZT”), or a three-component composition in which a third component is added to PZT of the two-component composition. A ferroelectric material utilizing a two-component PZT is described in Applied Physics Letters, 1991, vol. 58, No. 11, pp 1161-1163.
A ferroelectric thin film of such metal oxide type can be prepared, for example, by a sputtering, an MOCVD or a sol-gel method. The sol-gel method is executed by coating a substrate with a solution containing a hydrolysable compound of each raw material metal, a partially hydrolyzed product thereof or a partially polycondensed product thereof, then drying and heating the coated film in the air to form a metal oxide film, and executing a sintering at a crystallizing temperature or higher of the metal oxide to crystallize the film, thereby obtaining a ferroelectric thin film. As the hydrolysable metal compound for the raw material, an organic compound is generally employed, such as a metal alkoxide, a partially hydrolyzed product thereof or a partially polycondensed product thereof. The sol-gel method allows to obtain a ferroelectric film most inexpensively and most simply.
As a method similar to the sol-gel method, there is known a metalorganic decomposition (MOD) method. The MOD method is executed by coating a substrate with a solution containing a hydrolysable metalorganic compound, such as a β-diketone complex or a carboxylate salt of a metal, then heating the coated film in the air or in oxygen to achieve a solvent evaporation of the coated film and a pyrolysis of the metal compound to form a metal oxide film, and executing a sintering at a crystallizing temperature or higher to crystallize the film. In the present invention, the sol-gel method, the MOD method and any combination thereof will be collectively referred to as “sol-gel method”.
Also, an ink jet recording head utilizing a piezoelectric element formed by the sol-gel method is disclosed. For example, Japanese Patent Application Laid-Open Nos. H09-092897, H10-139594 and H10-290035 disclose a process based on the sol-gel method, of coating a sol containing a piezoelectric material in plural divided portions on a lower electrode and repeating a heating process thereby forming a piezoelectric film of a piezoelectric element usable in an ink jet recording head.
Also various proposals have been made, as disclosed in Japanese Patent Application Laid-Open Nos. H09-092897, H10-139594 and H10-290035, for improving characteristics and operation reliability of the piezoelectric element employed as an actuator, in order to achieve an improvement in the performance and the durability of the ink jet recording head.
A piezoelectric material obtained by the sol-gel method is known to assume a columnar polycrystalline structure. The columnar structure is a structure in which a grain boundary is formed substantially perpendicularly to a direction along the thickness of the film, and has surface irregularities corresponding to the grain size. Such irregularities may cause an interfacial roughness to an upper electrode, thereby resulting in an increased leak current or a deterioration in the piezoelectric characteristics.
Also a prior piezoelectric element employ, as a lower electrode, a precious metal such as Ru or Pt or an oxide thereof, and an interfacial mismatching between the piezoelectric film and the lower electrode may cause a deterioration of electrical characteristics, such as an increased leak current or a loss in the dielectric breakdown resistance. Also in a piezoelectric element of a prior configuration, a perovskite type oxide such as barium titanate, strontium titanate or calcium titanate employed as the lower electrode may result in a deterioration of characteristics, particularly a displacement amount, of the piezoelectric film, because of a higher resistance of the electrode in comparison with the case of the precious metal. Furthermore, in the piezoelectric element of the prior configuration, an in-plane stress may be concentrated on a junction interface of a vibrating plate and a lower electrode, thereby leading to a peeling in a thermal treatment step in the manufacture or when the element is driven.